Sudoku
Pick how hard you want it, press New puzzle, and solve it here or print it out. Every puzzle has exactly one solution.
Nothing is marked while you fill it in. When every square has a digit in it, press Check to find out whether you have it. The clock starts when you type your first digit.
Time
0:00
The grid above prints without the controls, so it can be solved on paper. Print with solution adds an answer sheet on a second page.